Generally speaking, there are many applications in diverse fields where it is necessary or desirable to control fuel flow. Such applications and fields are widespread and often have significantly different requirements or parameters that must be met for successful operation of the device being supplied with fuel. As a result, the art is replete with fuel flow control devices directed to a number of problems encountered in each of such applications and fields.
By way of example, Gayfer et al U.S. Pat. No. 3,976,310 discloses what can only be described as an unusually complex fuel flow control system. It apparently utilizes a bellows and fluted rod as a pilot to control differential pressure across a metering area which is typical of high volume flow applications for main engines such as those on a helicopter or the like. As an indication of the complexity of the fuel flow control system, Gayfer et al use a centrifugal pump, gears, a flyweight control, etc.
In addition, Gayfer et al operates by sensing compressor discharge pressure. Thus, their fuel flow control system utilizes two restrictors which, if clogged, will render the unit entirely inoperable. Further, because of the use of lip seals, the fluted rod must be rotated in order to prevent stiction.
Because of the need to rotate the fluted rod, the Gayfer et al device cannot be located remote from the fuel pump which is desirable for some applications. This also follows because of the fact that the Gayfer et al device requires a return flow to the fuel pump inlet. As a result, the Gayfer et al device cannot be located close to a combustor which would be advantageous in order to minimize line filling during startup.
In view of the foregoing, the Gayfer et al device would be entirely unsuitable for utilization in low fuel flow applications. For instance, this type of device, which might be suitable for main engine applications, could not be commercially utilized for combustors in small auxiliary power units and the like. In fact, there has been no entirely satisfactory flow control device that can be located at a fuel delivery point for low fuel flow applications.
The present invention is directed to overcoming one or more of the foregoing problems and achieving one or more of the resulting objects.